The present invention relates to an image display apparatus and, more particularly, to a portable head-mounted image display apparatus which can be retained on the user's head or face.
Helmet- and goggle-type head-mounted image display apparatuses, which are designed to be retained on the user's head or face, have heretofore been developed for the purpose of enabling the user to enjoy virtual reality or a widescreen image by oneself.
Conventional head-mounted image display apparatuses, which are retained on the observer's head to project a virtual image in the air for observation, include one type in which a virtual image of a two-dimensional image display device, e.g., a liquid crystal display device, is formed by a combination of an optical path splitting device, e.g., a half-mirror or a beam splitter, and a concave ocular mirror, as disclosed, for example, in Japanese Patent Application Laid-Open (KOKAI) No. 03-191389 (1991). This type of head-mounted image display apparatus will be explained below with reference to the sectional view of FIG. 18. A beam splitter surface 4 is disposed in front of an eyeball position (eye point) 2 of an observer 1 so as to diagonally intersect the observer's visual axis 3. A concave ocular mirror 5 is disposed below the beam splitter surface 4 so as to extend substantially parallel to the visual axis 3, and a two-dimensional image display device 6 is disposed to face the concave ocular mirror 5 across the beam splitter surface 4. A reference axis 8 which intersects the visual axis 3 at right angles is disposed to extend through the display center 7 of the two-dimensional image display device 6 and also through the center of the concave ocular mirror 5. In this arrangement, light from the two-dimensional image display device 6 passes through the beam splitter surface 4 and is reflected by the concave ocular mirror 5 and then reflected by the beam splitter surface 4 to reach the eyeball position 2. Thus, a virtual image of the image displayed on the two-dimensional image display device 6 is formed in the air by the action of the concave ocular mirror 5, and the observer can view the displayed image. An outside, real world image can be viewed directly through the beam splitter surface 4.
The conventional head-mounted image display apparatus arranged as described above suffers, however, from the problem that the substrate of the two-dimensional image display device 6, e.g., a liquid crystal display device, is larger in size than the display screen thereof and hence interferes with the observer's head.
The problem of the conventional head-mounted image display apparatus will be explained below more specifically. The two-dimensional image display device 6 needs to raise the pixel density in the display screen thereof and to thereby increase the number of pixels per unit area in order to realize high-definition display. Therefore, it is necessary to achieve electrical connection by leading electric wirings for switching of the pixels to the outside of the display screen. When the number of pixels is 100,000, for example, the number of electrical connections required is 300. Therefore, the conventional practice is to fabricate a switching circuit at the periphery of the display screen to thereby reduce the number of electrical connections, i.e., to ten-odd connections. For the above-described reason, the substrate of the two-dimensional display device needs an area for electrical connection of the pixels with switching elements in addition to the area for display and requires a substrate larger in size than the display screen.
Thus, the half-mirror or beam splitter surface 4 must be disposed at a predetermined distance from the observer's eye 2 in order to prevent the substrate of the two-dimensional image display device 6 from interfering with the observer's head. Accordingly, when it is intended to widen the field angle for observation, the size of the half-mirror or beam splitter surface 4 increases, resulting in an increase in the overall size of the apparatus. In the case of a head-mounted image display apparatus such as that shown in FIG. 18, the increase of the size and weight is a principal factor in making the user feel uncomfortable when wearing the display apparatus, which is a serious problem.